Devices are known which are used to weld battery covers onto battery cases or jars. Such devices have, in the past, solved the problem of how to weld around terminal posts which extend upwardly beyond the plane established by the rim of the battery jar by employing one piece heating elements shaped to be equal to the size of the periphery of the jar rim a particular jar on which a cover is being welded. Such heating elements have either had a hollow interior or were provided with properly positioned holes through which the terminal posts could extend. Such heating elements were usually fed horizontally from alongside the welding area after the cover had been lifted completely off of the battery jar and out of engagement with the terminal posts. Following the insertion of the one piece heating platen from the side the platen and the cover would again be lowered over the terminal posts and back onto the jar with the platen now occupying a position between the upper edge of the jar and the bottom of the cover. Following heating, the battery cover would again be lifted completely off and away from the battery jar and the terminal posts so that the heating platen could be raised away from the jar and above the tops of the terminal posts after which it could be withdrawn horizontally with the cover being lowered thereafter into place so that the welding process could be completed.
The complete removal of the battery cover from the battery jar and its subsequent travel back and forth during heating and welding to allow for the insertion and removal of the heating platen complicates the welding process in a number of ways not the least of which is that when the cover is removed the initial alignment provided by having the cover in the jar is lost and additional alignment problems can result. It should be kept in mind that as the sidewall thickness of battery jars decreases there is a tendency for such sidewalls to flex inwardly or outwardly and, accordingly, at least to some extent, the cover helps stabilize and shape the sidewalls of the battery jar. When the cover is completely removed, it is possible for the sidewalls of the battery jar to become distorted so that during the heating process when the cover is not continuously in the jar, both the jar and the cover may be irregularly melted.
In addition, it is known that an oxidized surface can be formed on melted thermoplastic or plastic materials when exposed to air. Likewise, the heating of the plastic to its fusion temperature also tends to degrade the plastic adjacent the heating platen. Thus, the longer the melted surfaces remain exposed to the atmosphere the greater the problems associated therewith. Further, to produce clean and strong joints between the melted areas it is important to have clean nondegraded melted material within the joint. Accordingly, by raising the cover and waiting while the platen is removed and moving the cover back into the jar, even assuming acceptable alignment is again obtained, the relatively long period of time that both the jar and cover have to remain exposed increases the inevitability of having weld failures result due to the relatively long exposure times.
Also, since the platens were one piece elements, each could be shaped or sized for one or a small grouping of battery sizes. While there are two relatively standard width sizes for battery jars there are a wide variety of lengths used in industry. Accordingly, each change from one size or one group to another required such machines to be out of service for relatively long periods while the platens were exchanged and the machine recalibrated.
Accordingly, one of the primary objective of the present invention is to provide a device which will allow the welding of battery covers onto battery jars in a way that does not require the cover to be completely removed from the jar during the welding operation. An additional objective is the development of a welding device that allows the processing of a wide number of jar sizes, both with respect to the height of the jar and their length and width dimensions, by making it a relatively simple matter to change from one set of jar parameters to another in a short time.